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A sudoriferous gland, or simply sweat gland, is an exocrine gland in the human body responsible for producing perspiration, or sweat. The average person has between two and four million of these glands located in the dermis, or second layer of skin, throughout the body. Each gland has a coiled portion located beneath the skin that produces sweat, and a hollow tube portion that connects the gland to pores on the surface of the skin. There are two types of sweat gland: eccrine sweat glands, also called merocrine sweat glands, which are found all over the body; and apocrine sweat glands, which are found only in the armpits and genital area.
When stimulated by exercise, heat, or nerve signals, an eccrine sudoriferous gland secretes a clear, watery fluid that is similar in chemical composition to plasma. The fluid from the coiled portion of the gland then travels up the hollow duct portion towards the surface of the skin. As the perspiration fluid travels up this duct, two things can occur. In conditions where the person sweating is either in a cool place or at rest, the ducts absorb a large amount of the fluid and only a small amount of sweat reaches the surface of the skin. If the person sweating is hot or engaged in physical activity, the ducts cannot absorb the fluid quickly enough and a larger volume of sweat makes its way to the skin's surface.
An apocrine sudoriferous gland is different from the eccrine type of gland in many ways. Eccrine sweat glands are smaller and terminate in openings called pores. Apocrine sweat glands usually terminate in a hair follicle instead. The eccrine glands produce sweat from birth, while the apocrine glands are activated later in life, usually around the time of puberty. Sweat secreted by an apocrine sudoriferous gland is thick and cloudy and contains proteins and fatty acids that can be affected by various kinds of bacteria, which can cause unpleasant odors. Apocrine sweat gland secretions might also contain chemical messengers called pheromones.
The sudoriferous glands are important for the functioning of the human body because sweat is the body's primary natural cooling mechanism. Sweat that travels all the way to the skin's surface eventually evaporates, causing overall body temperature to decrease. Heat and exertion are not the only causes of sweating; emotional upset or stress can also cause a person to sweat by stimulating nerves that send signals to the sweat glands. The apocrine glands under the arms are particularly stimulated by stress, as are the eccrine glands in the palms of the hands.